/*
Copyright 2019 The Vitess Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package pools

import (
	"fmt"
	"sync"
	"time"

	"vitess.io/vitess/go/cache"
)

// Numbered allows you to manage resources by tracking them with numbers.
// There are no interface restrictions on what you can track.
type Numbered struct {
	mu                   sync.Mutex
	empty                *sync.Cond // Broadcast when pool becomes empty
	resources            map[int64]*numberedWrapper
	recentlyUnregistered *cache.LRUCache
}

type numberedWrapper struct {
	val            interface{}
	inUse          bool
	purpose        string
	timeCreated    time.Time
	timeUsed       time.Time
	enforceTimeout bool
}

type unregistered struct {
	reason           string
	timeUnregistered time.Time
}

func (u *unregistered) Size() int {
	return 1
}

//NewNumbered creates a new numbered
func NewNumbered() *Numbered {
	n := &Numbered{
		resources:            make(map[int64]*numberedWrapper),
		recentlyUnregistered: cache.NewLRUCache(1000),
	}
	n.empty = sync.NewCond(&n.mu)
	return n
}

// Register starts tracking a resource by the supplied id.
// It does not lock the object.
// It returns an error if the id already exists.
func (nu *Numbered) Register(id int64, val interface{}, enforceTimeout bool) error {
	// Optimistically assume we're not double registering.
	now := time.Now()
	resource := &numberedWrapper{
		val:            val,
		timeCreated:    now,
		timeUsed:       now,
		enforceTimeout: enforceTimeout,
	}

	nu.mu.Lock()
	defer nu.mu.Unlock()

	_, ok := nu.resources[id]
	if ok {
		return fmt.Errorf("already present")
	}
	nu.resources[id] = resource
	return nil
}

// Unregister forgets the specified resource.  If the resource is not present, it's ignored.
func (nu *Numbered) Unregister(id int64, reason string) {
	success := nu.unregister(id)
	if success {
		nu.recentlyUnregistered.Set(
			fmt.Sprintf("%v", id), &unregistered{reason: reason, timeUnregistered: time.Now()})
	}
}

// unregister forgets the resource, if it exists. Returns whether or not the resource existed at
// time of Unregister.
func (nu *Numbered) unregister(id int64) bool {
	nu.mu.Lock()
	defer nu.mu.Unlock()

	_, ok := nu.resources[id]
	delete(nu.resources, id)
	if len(nu.resources) == 0 {
		nu.empty.Broadcast()
	}
	return ok
}

// Get locks the resource for use. It accepts a purpose as a string.
// If it cannot be found, it returns a "not found" error. If in use,
// it returns a "in use: purpose" error.
func (nu *Numbered) Get(id int64, purpose string) (val interface{}, err error) {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	nw, ok := nu.resources[id]
	if !ok {
		if val, ok := nu.recentlyUnregistered.Get(fmt.Sprintf("%v", id)); ok {
			unreg := val.(*unregistered)
			return nil, fmt.Errorf("ended at %v (%v)", unreg.timeUnregistered.Format("2006-01-02 15:04:05.000 MST"), unreg.reason)
		}
		return nil, fmt.Errorf("not found")
	}
	if nw.inUse {
		return nil, fmt.Errorf("in use: %s", nw.purpose)
	}
	nw.inUse = true
	nw.purpose = purpose
	return nw.val, nil
}

// Put unlocks a resource for someone else to use.
func (nu *Numbered) Put(id int64, updateTime bool) {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	if nw, ok := nu.resources[id]; ok {
		nw.inUse = false
		nw.purpose = ""
		if updateTime {
			nw.timeUsed = time.Now()
		}
	}
}

// GetAll returns the list of all resources in the pool.
func (nu *Numbered) GetAll() (vals []interface{}) {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	vals = make([]interface{}, 0, len(nu.resources))
	for _, nw := range nu.resources {
		vals = append(vals, nw.val)
	}
	return vals
}

// GetOutdated returns a list of resources that are older than age, and locks them.
// It does not return any resources that are already locked.
func (nu *Numbered) GetOutdated(age time.Duration, purpose string) (vals []interface{}) {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	now := time.Now()
	for _, nw := range nu.resources {
		if nw.inUse || !nw.enforceTimeout {
			continue
		}
		if nw.timeUsed.Add(age).Sub(now) <= 0 {
			nw.inUse = true
			nw.purpose = purpose
			vals = append(vals, nw.val)
		}
	}
	return vals
}

// GetIdle returns a list of resurces that have been idle for longer
// than timeout, and locks them. It does not return any resources that
// are already locked.
func (nu *Numbered) GetIdle(timeout time.Duration, purpose string) (vals []interface{}) {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	now := time.Now()
	for _, nw := range nu.resources {
		if nw.inUse {
			continue
		}
		if nw.timeUsed.Add(timeout).Sub(now) <= 0 {
			nw.inUse = true
			nw.purpose = purpose
			vals = append(vals, nw.val)
		}
	}
	return vals
}

// WaitForEmpty returns as soon as the pool becomes empty
func (nu *Numbered) WaitForEmpty() {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	for len(nu.resources) != 0 {
		nu.empty.Wait()
	}
}

//StatsJSON returns stats in JSON format
func (nu *Numbered) StatsJSON() string {
	return fmt.Sprintf("{\"Size\": %v}", nu.Size())
}

//Size returns the current size
func (nu *Numbered) Size() int64 {
	nu.mu.Lock()
	defer nu.mu.Unlock()
	return int64(len(nu.resources))
}
